Benzylidene anabaseines act as high-affinity agonists for insect nicotinic acetylcholine receptors

Benzylidene anabaseines are agonists selective for vertebrate alpha7-nicotinic acetylcholine receptor (nAChR), while they exhibit antagonist activity toward vertebrate alpha4beta2-nAChR. To investigate the effects of benzylidene anabaseines on insect nAChRs, we performed [3H]epibatidine-binding assays and neurophysiological experiments using American cockroach (Periplaneta americana) nerve-cord preparations. Of the six compounds tested, 3-benzylideneanabaseine (BA) and 6'-chloro-3-benzylideneanabaseine (CBA) displayed the highest potency in the binding assays, with K(i)s of 35.0 and 21.2nM, respectively. The introduction of a nitro group at the 4-position of the phenyl group led to a decrease in affinity by two orders of magnitude, while that of a chlorine atom at the 6'-position had little effect on affinity. In neurophysiological experiments, BA at 3.3 microg/ml increased the spike frequency observed with the nerve preparation, as observed with nicotine at 16.6 microg/ml. These findings suggest that benzylidene anabaseines act as high-affinity agonists in P. americana nAChRs and that they might therefore prove useful as probes for insect nAChRs.